New strapped calix[4]pyrrole based receptor for anions

Calix[4]pyrrole bearing catechol-derived diether strap linked via alkyl chains has been synthesized and characterized for the first time. The strap with 1,2-diether link is providing a relatively constrained geometry on its side of the calix[4]pyrrole moiety. As a result only one isomer (cis-type) of the receptor formed during reaction. The crystal structure reveals two molecules of methanol bound to the host. This calix[4]pyrrole also exhibits enhanced binding towards halide anions compared to simple calix[4]pyrrole apart from showing binding towards dihydrogenphosphate and acetate ions. The association constants are quite similar to that found for orcinol strapped calix[4]pyrrole towards halide anions in general, but having a higher preference for chloride than bromide ion in particular. Further it shows very strong preference towards fluoride ion.

Receptor 4 was synthesized in three steps from catechol. In solid state it is bound to two methanol molecules. It displays strong affinity towards fluoride and chloride than bromide ion compared to related systems apart from showing moderately large binding toward acetate and dihydrogenphosphate ions.Figure optionsDownload as PowerPoint slideResearch highlights
► Catechol derived strapped calix[4]pyrrole synthesized.
► Two methanol molecules were bound to it in the solid state.
► Strong affinity towards fluoride and chloride ions was observed in acetonitrile.